The present invention relates to a system for controlling the clutch current of an electromagnetic clutch disposed between a crankshaft of an engine and an infinitely variable transmission of a motor vehicle.
In order to start the vehicle, the control system for the electromagnetic clutch is adapted to increase clutch current flowing in a coil of the electromagnetic clutch with respect to an increase of the engine speed. When vehicle speed exceeds a predetermined speed (for example 20 km/h), a lock-up current flows through the coil, so that the clutch is entirely engaged.
A power transmission system comprising the electromagnetic clutch and an infinitely variable belt-drive automatic transmission has been proposed. In the automatic transmission, various operating ranges such as D (driving)-range, Ds-range, N(neutral)-range, R(reverse)-range and P(parking)-range are provided and the selection of the range is done by a select lever. In the Ds-range, the transmission ratio is varied in a high engine speed range in order to provide powerful driving of the vehicle. Accordingly, select lever operation for the change from the D-range to the Ds-range or vice versa is often performed while driving. On the other hand, for the selection of the ranges, a D-range switch and a Ds-range switch are provided to be operated by the select lever. However, there is a dead range where no signal occurs between operation of the D-range switch and operation of the Ds-range switch during the operation of the select lever. Because of the dead range, the clutch current is cut off to disengage the automatic transmission from the engine, which means a cutting off of the power transmission while driving.